Plasma cutting tools used to cut or otherwise operate on a workpiece typically comprise a gas nozzle with an electrode therein. Generally, plasma tools direct gas through a nozzle toward the workpiece, with some or all the gas ionized in a plasma arc between the electrode and the workpiece. The arc is used to cut, mark or otherwise operate on the workpiece.
In most tools, a pilot arc is first established between the electrode and the nozzle. Then, the pilot arc is transferred from the nozzle to the workpiece for cutting and/or other operations. For example, some tools use contact-based starting, with the electrode and nozzle initially in contact with one another. While current is passing through the electrode and nozzle, the electrode and nozzle are moved apart to create a gap. A spark across the gap initiates the pilot arc in a successful starting operation.
Other tools use non-contact starting, which can advantageously avoid wear on the electrode that is aggravated by contact during starting and can also avoid the need to have more complexity in terms of additional moving parts to bring the nozzle and electrode into and out of contact. To initiate a plasma arc in a non-contact start, a high electric potential must be generated between the spaced apart nozzle (which acts as the anode) and the electrode (which acts as the cathode). The generated voltage must exceed the break over voltage associated with the air gap between the nozzle and electrode. The break over voltage can be influenced by factors such as distance between nozzle and electrode, type of gas present, velocity of gas flow, and nozzle and electrode geometry.
Plasma arc torches can be used to cut through a material or to mark a material by not cutting all the way through. Devices that perform both functions are often complex, including substantial parallel equipment for the cutting and the marking functions. Multiple power and gas supplies, multiple housings and control equipment elements are often required. Accordingly, a simplified and effective system for providing both cutting and marking function with a single gas, air cooled torch would be welcome.